GLYCOSYLINOSITOL PHOSPHOLIPID ANCHORS OF THE SCRAPIE AND CELLULAR PRION PROTEINS CONTAIN SIALIC-ACID

The only identified component of the scrapie prion is PrP(Sc), a glycosylinositol phospholipid (GPI)-linked protein that is derived from the cellular isoform (PrP(C)) by an as yet unknown posttranslational event. Analysis of the PrP(Sc) GPI has revealed six different glycoforms, three of which are unprecedented. Two of the glycoforms contain N-acetylneuraminic acid, which has not been previously reported as a component of any GPI. The largest form of the GPI is proposed to have a glycan core consisting of Man-alpha-Man-alpha-Man-(NeuAc-Gal-GalNAc-)Man-GlcN-Ino. Identical PrP(Sc) GPI structures were found for two distinct isolates or "strains" of prions which specify different incubation times, neuropathology, and PrP(Sc) distribution in brains of Syrian hamsters. Limited analysis of the PrP(C) GPI reveals that it also has sialylated glycoforms, arguing that the presence of this monosaccharide does not distinguish PrP(C) from PrP(Sc).